This invention relates to a measuring apparatus employing a sensing apparatus selectively monitoring the position of a sensing member and employing a variable differential transformer having a movable coupling element operatively connected to the sensing member.
There are many applications where it is desired to accurately monitor the location of a particular object with respect to some standard or reference. One such situation occurs in the fabrication of stator assemblies for electric motors wherein a series of laminations are individually stacked and aligned. One possible sequence of fabrication may include the compression of such stacked laminations by a press or other means which enables the individual laminations to be flattened and tightly engage one another before being interconnected and possibly sealed. When compressed into the configuration in which such laminations will take in the resultant stator assembly, it is extremely important to accurately measure the axial length to insure that such stacked laminations will have the appropriate electrical and physical characteristics for desirable operation within a motor. While it is preferrable to insure that each stack of laminations proceeding along a production line has an identical axial length, certain small production tolerances are allowable both under and over the specified axial lamination stack length. Of course, stator axial lengths exceeding predetermined limitations greater or less than the desired axial length necessitates the rejection of the fabricated stator stack. When compressing and monitoring a large number of lamination stacks, the axial length of a particular stack beyond predetermined limitations may be overlooked by an operator or may be inaccurately measured through human error, particularly where close tolerances are required. It is therefore desirable to have an apparatus which precisely measures the axial length of each lamination stack and additionally monitors deviations in axial stator length beyond predetermined over or under limitations from the desired length and provide a distinguishing warning to an operator indicating a required rejection of the monitored stack.
Variable differential transformers have been utilized in many applications for sensing or monitoring the position of a member. For example, linear variable differential transformer circuits have been proposed to provide dual ended outputs connected to a pair of corresponding absolute value circuits both of which are connected to a summing circuit output and a stabilizing amplifier, such as illustrated in Section 17-137, Electronics Engineers' Handbook, D. Fink and A. McKenzie, Copyright 1975. Other systems have employed a variable differential transformer in connection with full-wave rectification circuits employing static elements to supply an output signal proportional to the sensing member movement to a number of signal comparitors for comparison with pre-established reference signals, such as shown in the Houpt et al U.S. Pat. No. 3,354,399. Other systems have employed variable differential transformers for sensing the movement of a member by employing a differential transformer with a single ended output connected through a coupling transformer to provide a position responsive output signal, such as shown in the Torn et al U.S. Pat. No. 3,046,553. Other systems have employed positive and negative signal detectors arranged in a comparitor arrangement for providing outputs indicative of predetermined spaced positions of a movable member from a reference position in a differential transformer, such as shown in the Muir U.S. Pat. No. 3,684,961.